BUILD: compiler: fix __equals_1() on older compilers

BUILD: compiler: fix __equals_1() on older compilers

It appeared that __has_attribute() doesn't work on gcc 4.4 and older
because the concatenation of __has_attribute##x isn't resolved as a one
before being passed to __equals_1() which immediately concatenates it to
comma_for_one. We first need to pass it through an extra layer to resolve
this name to a value. The new version was tested with gcc 4.2 to 11.3.

This may be backported though it's pretty minor.